Phase-change memory device and method of manufacturing the same

ABSTRACT

In a method of forming a phase-change memory device, a variable resistance member may be formed on a s semiconductor substrate having a contact region, and a first electrode may be formed to contact a first portion of the variable resistance member and to be electrically connected to the contact region. A second electrode may be formed so as to contact a second portion of the variable resistance member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 2004-380, filed on Jan. 5, 2004, the contents of whichare incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a phase-change memory deviceand a method of manufacturing the phase-change memory device.

2. Description of the Related Art

As information technology rapidly develops, semiconductor devices havingsubstantially high response speed, substantially large storage capacityand substantially low power consumption are desired for portablecommunication devices designed to process a substantial amount of data.For example, these semiconductor devices may have the high responsespeed of a static random access memory (SRAM) device, non-volatilecharacteristics of a flash memory device, and high integration degree ofa dynamic random access memory (DRAM) device, even though thesemiconductor device may operate with low power consumption than a SRAM,flash memory and/or DRAM device.

Recently, research has begun in earnest into developing memory devicessuch as a ferroelectric random access memory (FRAM) device, a magneticrandom access memory (MRAM) device, a phase-change random access memory(PRAM) device and nano-floating gate memory (NFGM) device, since thesememory devices may operate with substantially lower power consumptionand may exhibit desired characteristics as related to writing datathereto, reading data therefrom and maintaining data therein. Amongthose memory devices, attention from a development and/or researchperspective has become focused on the PRAM device, because the PRAMdevice has a relatively high degree of integration and high responsespeed, etc., while having a relatively simple construction.Additionally, the PRAM device may be manufactured at a relatively lowercost as compared to other memory devices.

A phase-change memory device may include phase-change material having acrystalline structure- that may vary in accordance with a heat generatedby a current applied to the phase-change material. Phase-change materialemployed for the phase-change memory device may includes a chalcogenidematerial or alloy, for example, such as germanium-antimony-tellurium(Ge—Sb—Te, also referred to as ‘GST’). Phase-change material such as GSThas a crystalline structure that varies according to a heat caused by anamount and time of a current applied thereto. In general, amorphous GSThas a relatively high specific resistance, whereas crystalline GST has arelatively low specific resistance. Due to the resistance variationproperties of GST, a phase-change memory device including GST may storedata therein.

FIG. 1 is a cross-sectional view illustrating a conventionalphase-change memory device. Referring to FIG. 1, the conventionalphase-change memory device includes a data store element 47 in an activeregion of a semiconductor substrate 1 that has an isolation layer 3thereon to define the active region. Word lines 5 are provided on thesemiconductor substrate 1, with a first contact region 7 and a secondcontact region 9 provided at surface portions of the semiconductorsubstrate 1 between the word lines 5.

A lower insulating interlayer 21 may include a first insulatinginterlayer 11 and a second insulating interlayer 19 on the semiconductorsubstrate 1. A first contact hole 23 may be formed through the lowerinsulating interlayer 21 to expose the first contact region 7. A storageplug 27 including a first plug 13 and a second plug 25 may be providedin the first contact hole 23. The first plug 13 may be connected to thefirst contact region 7 and the second plug 25 may be positioned on thefirst plug 13, as shown in FIG. 1.

A bit line pad 15 contacting the second contact region 9 may be providedthrough first insulating interlayer 11, with a bit line 17 provided onthe bit line pad 15. The second insulating interlayer 19 may be formedon the semiconductor substrate 1 with the bit line 17 formed thereon.

The data store element 47 may be formed on the second insulatinginterlayer 19 of lower insulating interlayer 21. The data store element47 may include a first barrier layer pattern 29, a phase-change layerpattern 31 and a protection oxide layer pattern 33. The phase-changelayer pattern 31 may be formed of a phase-change material that has twostable phases according to a temperature variation thereof, such as GST,for example. The first barrier layer pattern 29 may be formed of a metalnitride so as not to react with the phase-change layer pattern 31. Toprevent an oxidation of the phase-change layer pattern 31, theprotection oxide layer pattern 33 may be formed with one of a siliconnitride, boron nitride, silicon carbide or zinc sulfide.

An upper insulating interlayer 35 covers the data store element 47, anda plate electrode contact hole 37 may be formed through the upperinsulating interlayer 35 to expose the phase-change layer pattern 31 ofthe data store element 47. A spacer 39 is provided on an inside of theplate electrode contact hole 37. A second barrier layer pattern 41 ofmetal nitride may be formed on the upper insulating interlayer 35 tofill the plate electrode contact hole 37. A plate electrode 43 may beformed on the second barrier layer pattern 41.

To write data to the data store element 47 of FIG. 1, a portion of thephase-change layer pattern 31 in contact with the second barrier layerpattern 41 may be converted into a crystalline or amorphous state, asshown FIG. 2A, when a current is applied to the phase-change layerpattern 31 so as to generate heat therein.

The conventional phase-change memory device has a vertical constructionin which the first barrier layer pattern 29, phase-change layer pattern31, second barrier layer pattern 41 and plate electrode 43 arevertically stacked on the semiconductor substrate 1. In thisconventional phase-change memory device with vertical construction, aphase-change region generated in a phase-change layer pattern 31 issubstantially small. This is because the phase-change region may beformed only at a portion of the phase-change layer pattern 31 that is incontact with an electrode (such as plate electrode 43 via second barrierlayer pattern 41). In addition, a relatively high current is applied tothe phase-change layer pattern 31 from the electrode so as to generateheat for sufficiently forming phase-change region in the phase-changelayer pattern 31. This problem is described in further detail withreference to FIGS. 2A and 2B.

FIG. 2A is a schematic cross-sectional view illustrating thephase-change region of the conventional phase-change memory device ofFIG. 1; and FIG. 2B is a schematic cross-sectional view illustrating atemperature distribution of the conventional phase-change memory deviceof FIG. 1. In FIG. 2B, the temperature distribution of the conventionalphase-change memory device is a simulated result obtained usingCFD-ACE+program provided by CFDRC Co. in U.S.A.

Referring to FIGS. 2A and 2B, in the conventional phase-change memorydevice with vertical construction as shown in FIG. 1, a phase-changeregion 55 is formed only at a minute portion of a phase-change layer 53that is in contact with a contact 51 (such as an electrode). Since heatcausing specific resistance variation of the phase-change region 55depends on current applied to the phase-change layer 53 from contact 51,the heat is generated in the phase-change layer 53 centering around aninterface between the phase-change layer 53 and the contact 51. That is,a temperature distribution Td causes the heat generated in thephase-change 53 to lean to the contact 51 centering the interfacebetween the phase-change layer 53 and the contact 51 as shown in FIG.2B. Thus, the heat generated in the phase-change region 55 may bedissipated through the contact 51, because the contact 51 (which may bea metal or a metal nitride, for example) has thermal conductivity aboutseven (7) times larger than that of the phase-change layer 53 (which maybe GST).

As heat dissipation occurs in the phase-change layer 53, more heat isthus required to generate the phase-change region 55 in the phase-changelayer 53 so that relatively high reset current is applied to thephase-change layer 53 from the contact 51 (a reset current is applied aspart of a reset operation to change state back from a relatively lowerspecific resistance crystalline state back to a relatively higherspecific resistance amorphous state). However, the relatively high resetcurrent may raise power consumption of the phase-change memory deviceand accelerate deterioration of the phase-change layer 53. Furthermore,because the temperature distribution Td leans toward the contact 51,temperature difference between the phase-change layer 53 and the contact51 increases so that the phase-change layer 53 may detach from thecontact 51.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention is directed to aphase-change memory device. The device may include a semiconductorsubstrate having a contact region with a variable resistance memberprovided on the semiconductor substrate. The device may include a firstelectrode contacting a first portion of the variable resistance memberand electrically connected to the contact region, and a second electrodecontacting a second portion of the variable resistance member.

Another exemplary embodiment of the present invention is directed to amethod of manufacturing a phase-change memory device. In the method, avariable resistance member may be formed on a semiconductor substratehaving a contact region, and a first electrode may be formed to contacta first portion of the variable resistance member and to be electricallyconnected to the contact region. A second electrode may be formed so asto contact a second portion of the variable resistance member.

Another exemplary-embodiment of the present invention is directed to aphase-change memory device. The device may include a semiconductorsubstrate having a contact region, with a lower wiring provided on thesemiconductor substrate and in contact with the contact region, and witha variable resistance member provided on the semiconductor substrate andseparated from the lower wiring. The device may include a firstelectrode contacting a first portion of the variable resistance memberand electrically connected to the lower wiring, a second electrodecontacting a second portion of the variable resistance member and aportion of an adjacent variable resistance member, and an upper wiringelectrically connected to the second electrode.

Another exemplary embodiment of the present invention is directed to amethod of manufacturing a phase-change memory device. In the method, acontact region may be formed on a semiconductor substrate, and a lowerwiring may be formed on the semiconductor substrate to electricallycontact the contact region. A variable resistance member may be formedon the semiconductor substrate so as to be separated from the lowerwiring. A first electrode may be formed so as to be electricallyconnected to the lower wiring and to contact a first portion of thevariable resistance member, and a second electrode may be formed thatcontacts a second portion of the variable resistance member and aportion of an adjacent variable resistance member. An upper wiring maybe formed to be electrically connected to the second electrode.

Another exemplary embodiment of the present invention is directed to aphase-change memory device. The device may include a semiconductorsubstrate having a contact region, a first electrode electricallyconnected to the contact region and a second electrode. The device mayinclude a variable resistance member provided between the first andsecond electrodes, the first and second electrodes positioned onsidewalls of the variable resistance member so as to enclose lateralportions of the variable resistance member.

Another exemplary embodiment of the present invention is directed to aphase-change memory device arrangement including two adjacentphase-change memory devices sharing a common semiconductor substrate.Each memory device may include a first electrode and a variableresistance member and may share a common second electrode between thecorresponding first electrodes. Each variable resistance member may beprovided between a corresponding first electrode and the common secondelectrode so that a portion of the common second electrode encloses afirst lateral portion of each of the two adjacent variable resistancemembers.

Another exemplary embodiment of the present invention is directed to amethod of manufacturing a phase-change memory device. A variableresistance member may be formed on a semiconductor substrate having acontact region. A first electrode may be formed so as to enclose a firstlateral portion of the variable resistance member, the first electrodebeing electrically connected to the contact region. A second electrodemay be formed so as to enclose a second lateral portion of the variableresistance member.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing, indetail, exemplary embodiments thereof with reference to the attacheddrawings, wherein like elements are represented by like referencenumerals, which are given by way of illustration only and thus do notlimit the exemplary embodiments of the present invention.

FIG. 1 is a cross-sectional view illustrating a conventionalphase-change memory device.

FIGS. 2A and 2B are schematic cross-sectional views illustrating aphase-change region of the conventional phase-change memory device.

FIG. 3 is a cross-sectional view illustrating a phase-memory device inaccordance with an exemplary embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a phase-change mechanismof a phase-change memory device in accordance with an exemplaryembodiment of the present invention.

FIG. 5A is a cross-sectional view illustrating a thermal distribution ofa phase-change memory device in accordance with an exemplary embodimentof the present invention.

FIG. 5B is a cross-sectional view illustrating a temperaturedistribution of a phase-change memory device in accordance with anexemplary embodiment of the present invention.

FIG. 6 is a graph illustrating reset current relative to areas ofcontact regions of a conventional phase-change memory device and aphase-change memory device in accordance with an exemplary embodiment ofthe present invention.

FIGS. 7A to 7I are cross-sectional views illustrating a method ofmanufacturing a phase-change memory device in accordance with anexemplary embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a phase-change memorydevice in accordance with another exemplary embodiment of the presentinvention.

FIGS. 9A to 9D are cross-sectional views illustrating a method ofmanufacturing a phase-change memory device in accordance with anotherexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set forth herein; rather, these exemplaryembodiments are provided so that this disclosure will be through andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the thickness of layers and regionsmay be exaggerated for clarity. Like reference numerals refer to similaror identical elements throughout. It will be understood that when anelement such as a layer, region or substrate is referred to as being“on” or “onto” another element, it may be directly on the other elementor intervening elements may also be present there between.

FIG. 3 is a cross-sectional view illustrating a phase-memory device inaccordance with one embodiment of the present invention. Additionallyhereafter, occasional reference may be made to FIGS. 7A, 7C and 7F indescribing FIG. 3. Referring to FIG. 3, the exemplary phase-changememory device may include a semiconductor substrate 100 having a firstcontact region 121 and a second contact region 124, a first lower wiring154, a second lower wiring 157, a first electrode 187, a secondelectrode 190, and a variable resistance member 184. The first andsecond lower wirings 154 and 157 may be configured so as to make contactwith the first and second contact regions 121 and 124. The firstelectrode 187 may be electrically connected to the first lower wiring154. The second electrode 190 may be arranged adjacent to the firstelectrode 187, with variable resistance member 184 formed between thefirst and second electrodes 187 and 190 and arranged in a directionparallel to the substrate 100, as shown in FIG. 3, for example.

An isolation layer 103 may be formed on the semiconductor substrate 100to define an active region thereon. Underlying structures, for examplegate structures 118, may be formed in the active region of the substrate100.

The first and second contact regions 121 and 124 may be formed atportions of the substrate 100 that are exposed between the underlyinggate structures 118. Each of the gate structures 118 may include a gateoxide layer pattern 106, a gate conductive layer pattern 109, a gatemask 112 and a spacer 115, as shown in FIG. 7A. The gate oxide layerpattern 106, the gate conductive layer pattern 109 and the gate mask 112may be sequentially formed on the substrate 100. Additionally, thespacer 115 may be formed on sidewalls of the gate oxide layer pattern106, the gate conductive layer pattern 109 and the gate mask 112, asshown in FIG. 7A.

A first insulating interlayer 127 may be formed on the substrate 100 tocover the underlying gate structures 118. The first and second lowerwirings 154 and 157 may make contact with corresponding first and secondcontact regions 121 and 124 via first insulating interlayer 127. Thatis, given holes or openings may be formed through the first insulatinginterlayer 127 and filled with the first and second lower wirings 154and 157, thereby connecting the first and second lower wirings 154 and157 to the first and second contact regions 121 and 124. The firstinsulating interlayer 127 may be formed of one of tetra ethyl orthosilicate (TEOS), undoped silicate glass (USG), spin on glass (SOG), highdensity plasma-chemical vapor deposition (HDP-CVD) oxide, etc., orcombinations of one or more of these materials.

In an example, the first lower wiring 154 may include a first plug 142formed on the first contact region 121 and a first pad 145 formed on thefirst plug 142, as shown in FIG. 7C. Also, the second lower wiring 157may include a second plug 148 formed on the second contact region 124with a second pad 151 formed on the second plug 148. The first andsecond lower wirings 154 and 157 may be formed of a conductive materialsuch as polysilicon doped with impurities or a metal, for example,tungsten (W), aluminum (Al), tantalum (Ta), copper (Cu), etc., orcombinations of one or more of these materials.

A second insulating interlayer 160 may be formed on the first insulatinginterlayer 127 with the first and second lower wirings 154 and 157formed through second insulating layer 160. A third plug 166 in contactwith the first lower wiring 154 may also be formed through the secondinsulating interlayer 160. The second insulating interlayer 160 may beformed of TEOS, USG, SOG, HDP-CVD oxide, etc, or combination thereof.The third plug 166 may be formed of conductive materials such as dopedpolysilicon or a metal, and/or combinations thereof. For example, thethird plug 166 may be formed using W, Al, Ta, Cu or a combinationthereof.

As shown in FIG. 3, the first electrode 187 may be electricallyconnected to the first lower wiring 154 via the third plug 166, and thesecond electrode 190 may be electrically connected to an upper wiring205 via a fourth pad 202. the first and second electrodes 187 and 190may be formed by interposing the variable resistance member 184therebetween, and also may be arranged in the direction parallel to thesubstrate 100. As shown in FIG. 3, first electrode 187, second electrode190 and variable resistance member 184 are arranged on a common surface(second insulating layer 160) parallel to semiconductor substrate 100.Portions of the first and second electrodes 187 and 190 may bepositioned on sidewalls of the variable resistance member 184 to encloselateral portions of the variable resistance member 184. As shown in FIG.3, two first electrodes 187 share a common second electrode 190. Thatis, two adjacent phase-change memory devices share a common secondelectrode 190, but each phase-change memory devices include firstelectrodes 187. The second electrode 190 may have a generally U-shapedcross section that encloses lateral portions of two adjacent variableresistance members 184.

The first and second electrodes 187 and 190 may include a conductivematerial containing nitrogen (N), a metal, a metal silicide, etc.Exemplary conductive materials containing nitrogen may include titaniumnitride (TiN), tantalum nitride (TaN), molybdenum nitride (MoN), niobiumnitride (NbN), titanium-silicon nitride (TiSiN), titanium-aluminumnitride (TiAlN), titanium-boron nitride (TiBN), zirconium-siliconnitride (ZrSiN), tungsten-silicon nitride (WSiN), tungsten-boron nitride(WBN), zirconium-aluminum nitride (ZrAlN), molybdenum-silicon nitride(MoSiN), molybdenum-aluminum nitride (MoAlN), tantalum-silicon nitride(TaSiN), tantalum-aluminum nitride (TaAlN), titanium oxynitride (TiON),titanium-aluminum oxynitride (TiAlON), tungsten oxynitride (WON),tantalum oxynitride (TaON), etc. The first and second electrodes 187 and190 may include one of the above conductive materials orcombinations/mixtures thereof. Examples of suitable conductive metalsfor the first and second electrodes 187 and 190 may include one oftitanium, tungsten, molybdenum or tantalum, and examples of suitablemetal silicides for the first and second electrodes 187 and 190 includetitanium silicide (TiSi) or tantalum silicide (TaSi), or mixtures of oneor more of these metals and/or metal silicides.

The first and second electrodes 187 and 190 may each be embodied as ofsingle layer structures composed of a material containing nitrogen,metal, metal silicide, etc. Alternatively, the first and secondelectrodes 187 and 190 may have double layer structures of materialscontaining nitrogen, metal and metal silicide, for example.

The variable resistance member 184 may include a first insulation layerpattern 169, a phase-change layer pattern 178 and a second insulationlayer pattern 181 as shown in FIG. 7F. The first insulation layerpattern 169, the phase-change layer pattern 178, and the secondinsulation layer pattern 181 may be successively formed on the secondinsulating interlayer 160.

The first and second insulation layer patterns 169 and 181 may includeoxide such as silicon oxide or nitride such as silicon nitride. Thephase-change layer pattern 178 may include a chalcogenide. For example,the phase-change layer pattern 178 may include chalcogenide alloys suchas germanium-antimony-tellurium (Ge—Sb—Te), arsenic-antimony-tellurium(As—Sb—Te), tin-antimony-tellurium (Sn—Sb—Te), ortin-indium-antimony-tellurium (Sn—In—Sb—Te),arsenic-germanium-antimony-tellurium (As—Ge—Sb—Te). Alternatively, thephase-change layer pattern 178 may include an element in GroupVA-antimony-tellurium such as tantalum-antimony-tellurium (Ta—Sb—Te),niobium-antimony-tellurium (Nb—Sb—Te) or vanadium-antimony-tellurium(V—Sb—Te) or an element in Group VA-antimony-selenium such astantalum-antimony-selenium (Ta—Sb—Se), niobium-antimony-selenium(Nb—Sb—Se) or vanadium-antimony-selenium (V—Sb—Se). Further, thephase-change layer pattern 178 may include an element in GroupVIA-antimony-tellurium such as tungsten-antimony-tellurium (W—Sb—Te),molybdenum-antimony-tellurium (Mo—Sb—Te), or chrome-antimony-tellurium(Cr—Sb—Te) or an element in Group VIA-antimony-selenium such astungsten-antimony-selenium (W—Sb—Se), molybdenum-antimony-selenium(Mo—Sb—Se) or chrome-antimony-selenium (Cr—Sb—Se).

Although the phase-change layer pattern 178 is described above as beingformed primarily of ternary phase-change chalcogenide alloys, thechalcogenide alloy of the phase-change layer pattern 178 could beselected from a binary phase-change chalcogenide alloy or a quarternaryphase-change chalcogenide alloy. Exemplary binary phase-changechalcogenide alloys may include one or more of Ga—Sb, In—Sb, In—Se,Sb₂—Te₃ or Ge—Te alloys; exemplary quarternary phase-change chalcogenidealloys may include one or more of an Ag—In—Sb—Te, (Ge—Sn)—Sb—Te,Ge—Sb—(Se—Te) or Te₈₁—Ge₁₅—Sb₂—S₂ alloy, for example.

In an example, the variable resistance member 184 may have a rectangularbox structure (i.e., be shaped generally in the shape of a box). As heatis generated in the phase-change layer pattern 178 due to a currentapplied thereto through the first electrode 187, the first and secondinsulation layer patterns 169 and 181 confine the heat to thephase-change layer pattern 178. That is, the variable resistance member184 may have a heat-confining ability in which the heat due to theapplied current is confined within the phase-change layer pattern 178heat dissipation from the phase-change layer pattern 178. This may bepossible since upper and lower portions of the phase-change layerpattern 178 are enclosed by first and second insulation layer patterns169 and 181.

FIG. 4 is a cross-sectional view illustrating a phase-change mechanismof a phase-change memory device in accordance with an exemplaryembodiment of the present invention.

Referring to FIG. 4, a phase-change layer pattern 233 is shownhorizontally contacting an electrode 230. Here, the electrode 230 mayhave a cross-sectional area S1 substantially larger than across-sectional area S2 of the phase-change layer pattern 233. Since thecross-sectional area S2 of the phase-change layer pattern 233 isnarrower than the cross-sectional area S1 of the electrode 230, densityof a current applied from the electrode 230 may be high at thecross-section of the phase-change layer pattern 233. Additionally, heatcaused by a reset current may be confined in the phase-change layerpattern 233 without a dissipation of heat from the phase-change layerpattern 233 to thereby efficiently form a phase-change region in thephase-change layer pattern 233. In other words, the phase-change layerpattern 233 of the present invention has a ‘self-heat confined’structure in which the heat for forming the phase-change region may beconfined in the phase-change layer pattern 233. This is because thephase-change region of the phase-change layer pattern 233 is separatedfrom the electrode 230 and the cross-sectional area S2 of thephase-change layer pattern 233 is substantially smaller than that of theelectrode 230. This may enable the exemplary phase-change memory deviceto use a reset current that may be considerably lower than the restcurrent required of the conventional phase-change memory device.

FIG. 5A is a cross-sectional view illustrating a phase-change region ofa phase-change memory device in accordance with one embodiment of thepresent invention, and FIG. 5B is a cross-sectional view illustrating atemperature distribution of the phase-change memory device in accordancewith one embodiment of the present invention. FIGS. 5A and 5B areprovided to describe the phase-change mechanism of the phase-changememory device.

In FIG. 5B, the temperature distribution of the phase-change memorydevice may be shown as a simulated result obtained using CFD-ACE+programprovided by CFDRC Co. in U.S.A., for example. Referring to FIGS. 5A and5B, the exemplary phase-change memory device may include a firstelectrode 240, a phase-change layer 243 and a second electrode 246 whichare horizontally disposed over a substrate. To prevent dissipation ofheat generated in the phase-change layer 243, a first insulation pattern249 and a second insulation pattern 252 may be formed on upper face ofthe phase-change layer 243 and beneath a bottom face of the phase-changelayer 243. If the first and second electrodes 240 and 246 are formed oftitanium nitride and the phase-change layer 243 is formed of GST, thecurrent density of the current applied from the first and secondelectrodes 240 and 246 increases in the phase-change layer 243 becausethe phase-change layer 243 has a cross-sectional area substantiallysmaller than those of the first and second electrodes 240 and 246. Inaddition, a phase-change region may be formed from a central portion ofthe phase-change layer 243 toward the first and second electrodes 240and 246. As shown in FIG. 5B, heat for forming a phase-change region 255does not dissipate from the phase-change layer 243 because a temperaturedistribution Td is uniform substantially centering the phase-changeregion 255 in a central portion of the phase-change layer 243.

In the conventional phase-change memory device of FIGS. 2A and 2B, heatfor forming the phase-change region 55 is dissipated through the contact51. Thus, additional, higher reset current is required to sufficientlyform the desired phase-change region 55 within the phase-change layerpattern 31. However, in the exemplary phase-change memory device, asevident by FIG. 5B, the phase-change region 243 may be formed in agenerally central portion of the phase-change layer 243. This may bepossible because the heat due to a reset current is confined in thephase-change layer 243 and separated from the first and secondelectrodes 240 and 246 by a given interval. Therefore, the phase-changememory device in accordance with the exemplary embodiments of thepresent invention may form the phase-change region 255 with a resetcurrent that is substantially lower than that of the conventionalphase-change memory device. Also, since the first and second insulationpatterns 249 and 252 are respectively formed on the upper face andbeneath the bottom face of the phase-change layer 243, the first andsecond insulation layer patterns 249 and 252 may additionally confinethe heat generated in the phase-change layer 243 without dissipation ofheat.

FIG. 6 is a graph illustrating reset currents relative to contact areasto compare the phase-change memory device of the present invention witha conventional phase-change memory device. In FIG. 6, the reset currentof the phase-change memory device was obtained by varying a width of aphase-change layer having a length of about 200 nm and a thickness ofabout 30 nm.

Referring to FIG. 6, when the phase-change layer has a cross-sectionalarea substantially identical to that of an electrode, the phase-changememory device of the present invention (shown by curve B) may beoperated using a reset current less than half of that used in theconventional phase-change memory device (shown by curve A).

Referring now to FIG. 3, a third insulating interlayer 196 may beprovided on the second insulating interlayer 160 to cover the variableresistance member 184, first electrode 187 and second electrode 190. Anupper wiring 205 may be provided on the third insulating interlayer 196.The upper wiring 205 is electrically connected to the second electrode190 through a fourth plug 202 formed through the third insulatinginterlayer 196. The fourth plug 202 and the upper wiring 205 may includea conductive material such as doped polysilicon, tungsten, aluminum,copper, tantalum, etc., and/or mixtures of one or more of theseconductive materials.

FIGS. 7A to 7I are cross-sectional views illustrating a phase-changememory device in accordance with one embodiment of the presentinvention. Hereinafter, a method of manufacturing a phase-change memorydevice will be described with reference to the FIGS. 7A to 7I.

Referring to FIG. 7A, an isolation layer 103 may be formed on asemiconductor substrate 100 to define an active region on thesemiconductor substrate 100. The isolation layer 103 may be formed by ashallow trench isolation (STI) process or a local oxidation of silicon(LOCOS) process, for example, although it is evident to those ofordinary skill in the art that other known processes could be used toform isolation layer 103.

A gate oxide layer, gate conductive layer and gate. mask layer may besequentially formed on the active region of the semiconductor substrate100, and then successively patterned by a photolithographic process,thereby forming a gate oxide layer pattern 106, a gate conductive layerpattern 109 and a gate mask 112 on the semiconductor substrate 100. Thegate conductive layer may have a single layer structure of polysilicondoped with impurities or metal, or alternatively may have a double layerconstruction including polysilicon doped with impurities and a metal.The gate mask layer may be formed using material that has an etchingselectivity relative to oxide. For example, the gate mask layer may beformed using nitride such as silicon nitride (SiN).

In an example, the gate mask layer may be partially etched by aphotolithography process to form the gate mask 112 on the gateconductive layer. Then, the gate conductive layer and the gate oxidelayer may be partially etched using the gate mask 112 as an etching maskto thereby form the gate conductive layer pattern 109 and the gate oxidelayer pattern 106.

A nitride layer including silicon nitride may be formed on thesemiconductor substrate 100 to cover the gate mask 112. The nitridelayer may be partially etched to form a gate spacer 115 on a sidewall ofa gate structure 118 that includes the gate oxide layer pattern 106, thegate conductive layer pattern 109 and the gate mask 112. The gate spacer115 may be formed by anisotropically etching the nitride layer, forexample.

Referring to FIG. 7B, a first contact region 121 and a second contactregion 124 may be formed at portions of the semiconductor substrate 100exposed between the gate structures 118 using the gate structures 118 asion implantation masks. That is, the first contact region 121(corresponding to a source region) and second contact region 124(corresponding to a drain region) may be formed by implanting impuritiesinto the portions of the substrate 100 and thermally treating theimplanted impurities. Accordingly, transistors including the gatestructures 118 and the first and second contact regions 121 and 124 maythus be formed on the semiconductor substrate 100, with the firstcontact region 121 representing the source region of the transistor andthe second contract region 124 representing the drain region of thetransistor.

A first insulating interlayer 127 may be formed on the substrate 100 tosubstantially cover the transistors. The first insulating interlayer 127may be composed of oxides such as tetra ethyl ortho silicate (TEOS),undoped silicate glass (USG), spin on glass (SOG), high densityplasma-chemical vapor deposition (HDP-CVD) oxide, etc. These can be usedalone or in a mixture thereof. In an example, the first insulatinginterlayer 127 may be planarized by a chemical mechanical polishing(CMP) process, an etch back process, or a combination process of a CMPand an etch back.

The first insulating interlayer 127 may be partially etched by aphotolithographic process to form a first opening 130 and a secondopening 133 through portions of the first insulating interlayer 127below which the first and second contact regions 121 and 124 arepositioned. The portions of the first insulating interlayer 127including the first and second openings 130 and 133 may be successivelyetched to thereby form a first contact hole 136 and a second contacthole 139 exposing corresponding first and second contact regions 121 and124. Alternatively, after spacers are formed on insides of the first andsecond openings 130 and 133 with a material having an etchingselectivity relative to oxide, portions of the first insulatinginterlayer 127 may be etched by a self-alignment process relative to thespacers to form first and second contact holes 136 and 139 exposing thefirst and second contact regions 121 and 124.

Referring to FIG. 7C, a first conductive layer may be formed on thefirst insulating interlayer 127 to fill the first and second contactholes 136 and 139 and to simultaneously fill the first and secondopenings 130 and 133. The first conductive layer may be formed with aconductive material such as doped polysilicon or metal like copper,tantalum, tungsten, aluminum, etc., singly or as a combination of on ormore of these materials.

Using a chemical mechanical polishing (CMP) process, an etch backprocess or a combination process of a CMP and an etch back, for example,the first conductive layer is partially removed until the firstinsulating layer 127 is exposed. Thus, a first plug 141 may be formed inthe first contact hole 136 and a first pad 143 may be formed in thefirst opening 130. At the same time, a second plug 148 and a second pad151 may be formed in the second contact hole 139 and the second opening133.

As a result, a first lower wiring 154 may be formed so as to contact thefirst contact region 121 and a second lower wiring 157 may be formed soas to contact the second contact region 124. The first lower wiring 154includes the first plug 142 formed on the first contact region 121 andthe first pad 145 formed on the first plug 142. The second lower wiring157 includes the second plug 148 formed on the second contact region 124and the second pad 151 formed on the second plug 148. The firstelectrode 187 (see FIG. 7G) may be successively formed so as to beelectrically connected to the first contact region 121 through the firstpad 145 and the first plug 142.

In an example, the first and second contact holes 136 and 139 may bedirectly formed through the first insulating interlayer 127 to exposecorresponding first and second contact regions 121 and 124 withoutforming the first and second openings 130 and 133. Then, the first andsecond contact holes 136 and 139 may be filled with a conductivematerial, thereby forming the first and second plugs 142 and 148. Here,the first and second lower wirings 154 and 157 may include correspondingfirst and second plugs 142 and 148, except the first and second pads 145and 151.

Referring to FIG. 7D, the second insulating interlayer 160 may be formedon the first insulating interlayer 127 where the first and second lowerwirings 154 and 157 are formed. The second insulating interlayer 160 maybe formed with one of TEOS, USG, SOG, HDP-CVD oxide, etc., and/orcombinations of one or more of these materials. The second insulatinginterlayer 160 may be partially etched by a photolithographic process toform a third contact hole 163 exposing the first pad 145 of the firstlower wiring 154 through the second insulating interlayer 160.

A second conductive layer may be formed on the second insulatinginterlayer 160 to fill the third contact hole 163. The second conductivelayer may be formed with a conductive material such as dopedpolysilicon, with a metal such as tantalum, copper, tungsten, aluminum,etc., and/or with mixtures of one or more metals, conductive materialsor combination of metals and conductive materials. In an example, afterthe second insulating interlayer 160 is planarized by a CMP process,etch back process or combination process of a CMP and an etch back, thesecond conductive layer may be formed on the planarized secondinsulating interlayer 160.

A third plug 166 filling the third contact hole 163 may be formed bypartially removing the second conductive layer until the secondinsulating interlayer 160 is exposed. The third plug 166 electricallyconnects the first lower wiring 154 to the first electrode 187.

Referring to FIG. 7E, a first insulation layer may be formed on thethird plug 166 and the second insulating interlayer 160. The firstinsulation layer may then be partially etched by a photolithographicprocess to form a first insulation layer pattern 169 on the secondinsulating interlayer 160. The first insulation layer pattern 169 may beformed using an insulation material such as oxide. The first insulationlayer pattern 169 may be separated from the third plug 166 by a givendistance.

A phase-change layer 172 and a second insulation layer 175 may besequentially formed on the second insulating interlayer 160 and thethird plug 166 to cover the first insulation layer pattern 169. Thephase-change layer 172 may be formed with a chalcogenide alloy by asputtering process. Here, the chalcogenide alloy may be a ternaryphase-change chalcogenide alloy such as Ge—Sb—Te (GST), As—Sb—Te,Sn—Sb—Te, Sn—In—Sb—Te, As—Ge—Sb—Te, etc. Additionally, the chalcogenidealloy may include an element in Group VA-antimony-tellurium such asTa—Sb—Te, Nb—Sb—Te, V—Sb—Te, etc., or an element in GroupVA-antimony-selenium such as Ta—Sb—Se, Nb—Sb—Se, V—Sb—Se, etc. Further,the chalcogenide alloy may include an element in GroupVIA-antimony-tellurium such as W—Sb—Te, Mo—Sb—Te, Cr—Sb—Te, etc., or anelement in Group VIA-antimony-selenium such as W—Sb—Se, Mo—Sb—Se,Cr—Sb—Se, etc. In an example, the phase-change layer 172 may be formedwith GST and the second insulation layer 175 may be formed with an oxidesuch as silicon oxide or a nitride such as silicon nitride, for example.

Although the phase-change layer 172 is described above as being formedof a ternary phase-change chalcogenide alloy, the phase-change layer 172could be formed of a binary phase-change chalcogenide alloy or aquarternary phase-change chalcogenide alloy. Exemplary binaryphase-change chalcogenide alloys may include one or more of Ga—Sb,In—Sb, In—Se, Sb₂—Te₃ or Ge—Te alloys; exemplary quarternaryphase-change chalcogenide alloys may include one or more of anAg—In—Sb—Te, (Ge—Sn)—Sb—Te, Ge—Sb—(Se—Te) or Te₈—Ge₁₅—Sb₂—S₂ alloy, forexample.

Referring to FIG. 7F, the second insulation layer 175 and thephase-change layer 172 may be successively etched by a photolithographicprocess to form a phase-change layer pattern 178 and a second insulationlayer pattern 181 on the first insulation layer pattern 169. Thus, avariable resistance member 184 including the first insulation layerpattern 169, phase-change layer pattern 178 and second insulation layerpattern 181 may be formed on the second insulating interlayer 160. Thevariable resistance member 184 may be separated from the third plug 166by the given distance as discussed above with respect to FIG. 7E. Asdescribed above, because the variable resistance member 184 has aself-heat confined structure that includes the first insulation layerpattern 169, phase-change layer pattern 178 and second insulation layerpattern 181, heat due to the reset current applied to the phase-changelayer pattern 178 may not be dissipated externally, but confined in thephase-change layer pattern 178.

Referring to FIG. 7G, a third conductive layer may be formed on thethird plug 166 and second insulating interlayer 160 to cover thevariable resistance member 184. The third conductive layer may be formedby a suitable deposition process such as a CVD process, a physical vapordeposition (PVD) process, an atomic layer deposition (ALD) process, etc.In addition, the third conductive layer may be formed of a conductivematerial containing nitrogen, metal, metal silicide, etc. Examples ofthe conductive material containing nitrogen may include TiN, TaN, MoN,NbN, TiSiN, TiAlN, TiBN, ZrSiN, WSiN, WBN, ZrAlN, MoSiN, MoAlN, TaSiN,TaAlN, TiON, TiAlON, WON, TaON, etc, singly or as a combination ormixture of one or more of these materials. The metal for the thirdconductive layer may include one of Ti, W, Mo, Ta, etc. The metalsilicide may be selected from one of TiSi and TaSi. The conductivematerial may be embodied as a single metal or metal silicide, orcombination of one or more metals or metals with metal silicides. In anexample, the third conductive layer may be composed of titanium nitride.In another example, the third conductive layer may have a double layeror a multi-layered structure that includes a conductive material filmcontaining nitrogen, a metal film and/or a metal silicide film, forexample.

The third conductive layer may be partially etched to form a firstelectrode 187 and a second electrode 190. In an example, the first andsecond electrodes 187 and 190 may be formed simultaneously. The firstelectrode 187 extends from the third plug 166 to a first portion of thevariable resistance member 184, whereas the second electrode 190 extendsfrom a second portion of one variable resistance member 184 to a secondportion of an adjacent variable resistance member 184, as shown in FIG.7G. As shown in FIG. 7G, two first electrodes 187 may be provided.Another first electrode 187 may be formed from a first portion of theadjacent variable resistance member 184 to another third plug 166. Forexample, the first and second portions of the variable resistance member184 correspond to both lateral portions thereof, respectively. That is,the first and second electrodes 187 and 190 respectively enclose a firstand a second lateral portions of the variable resistance member 184having a rectangular box shape. An upper face of the variable resistancemember 184 may be partially exposed between the first and secondelectrodes 187 and 190.

Referring to FIG. 7H, a third insulating interlayer 196 may be formed onthe second insulating interlayer 160 to cover the first electrode 187,second electrode 190 and the variable resistance member 184. The thirdinsulating interlayer 196 may be partially etched by a photolithographicprocess to form a fourth contact hole 199 exposing the second electrode190. Alternatively, after the third insulating interlayer 196 may beplanarized by a CMP process, an etch back process or a combination of aCMP and an etch back, the fourth contact hole 199 may be formed throughthe planarized third insulating interlayer 196.

Referring to FIG. 7I, a fourth conductive layer may be formed on thethird insulating interlayer 196 to fill the fourth contact hole 196. Thefourth conductive layer may be formed with a conductive material such asdoped polysilicon or a metal such as tungsten, copper, aluminum,tantalum, etc., of a single conductive material or metal or mixturesthereof. Hence, a fourth plug 202 may be formed in the fourth contacthole 199 so as to contact the second electrode 190, and an upper wiring205 may be simultaneously formed on the third insulating interlayer 196.The fourth plug 202 electrically connects the upper wiring 205 to thesecond electrode 190. Alternatively, after filling the fourth contacthole 199 with the fourth plug 202, the upper wiring 205 may be formed onthe fourth plug 202 and third insulating interlayer 196.

FIG. 8 is a cross-sectional view illustrating a phase-change memorydevice in accordance with another embodiment of the present invention.the phase-change memory device of FIG. 8 has elements substantiallyidentical to those of the phase-change memory device in FIG. 3, exceptthe variable resistance member 184 has a generally pyramidalcross-section (i.e., has a generally pyramidal shape).

Referring to FIG. 8, the phase-change device includes a semiconductorsubstrate 100 with a first contact region 121 and a second contactregion 124, a first lower wiring 154 in contact with the first contactregion 121, a second lower wiring 157 in contact with the second contactregion 124, a first electrode 187 electrically connected to the firstlower wiring 154, a second electrode 190 corresponding to the firstelectrode 187, and the variable resistance member 184 formed betweenfirst electrode 187 and the second electrode 190. The variableresistance member 184 may be arranged in a direction parallel to thesemiconductor substrate 100.

The variable resistance member 184 may include a first insulation layerpattern 169, a phase-change layer pattern 178 and a second insulationlayer pattern 181 sequentially formed on a second insulating interlayer160, as shown in more detail in FIG. 9B. The first insulation layer 169may have an area that is substantially wider than that of thephase-change layer pattern 178, and the phase-change layer pattern 178may have an area substantially larger than that of the second insulationlayer pattern 181. As a result, the variable resistance member 184 hasthe pyramidal structure including lateral portions with a given slope.

The first electrode 187 may extend from a third plug 166 to a firstlateral portion of the sloped variable resistance member 184, whereasthe second electrode 190 may extended from a second lateral portion ofthe sloped variable resistance member 184 to a portion of an adjacentvariable resistance member 184. The first and second electrodes 187 and190 may be separated from each other on an upper face of the variableresistance member 184 so that the upper portion of the variableresistance member 184 is exposed between the first and second electrodes187 and 190. The second electrode 190 is electrically connected to anupper wiring 205 through a fourth plug 202 penetrating a thirdinsulating interlayer 166.

FIGS. 9A to 9D are cross-sectional views illustrating a method ofmanufacturing the phase-change memory device in FIG. 8. In thisexemplary embodiment, steps for forming the second insulating interlayer160 and the third plug 166 are substantially identical to thosedescribed with reference to FIGS. 7A to 7D and are not repeated here forreasons of brevity.

Referring to FIG. 9A, a first insulation layer 168, a phase-change layer172 and a second insulation layer 175 may be sequentially formed on thethird plug 166 and the second insulating interlayer 160. The first andsecond insulation layers 168 and 175 may be formed of an oxide such assilicon oxide or nitride like silicon nitride. The phase-change layer172 may be formed of a ternary phase-change chalcogenide alloy such asGST, As—Sb—Te, Sn—Sb—Te, Sn—In—Sb—Te, As—Ge—Sb—Te, Ta—Sb—Te, Nb—Sb—Te,V—Sb—Te, Ta—Sb—Se, Nb—Sb—Se, V—Sb—Se, W—Sb—Te, Mo—Sb—Te, Cr—Sb—Te,W—Sb—Se, Mo—Sb—Se, Cr—Sb—Se, etc. Alternatively, the phase-change layer172 could be formed of a binary phase-change chalcogenide alloy or aquarternary phase-change chalcogenide alloy, example alloys of whichhave been previously described above.

Referring to FIG. 9B, after a photoresist pattern (not shown) is formedon the second insulating interlayer 175, the second insulation layer175, the phase-change layer 172 and the first insulation layer 168 maybe successively etched using the photoresist pattern as an etching mask.Thus, a variable resistance member 184 including the first insulationlayer pattern 169, phase-change layer pattern 178 and the secondinsulation layer pattern 181 may be formed on the second insulatinginterlayer 160. The variable resistance member 184 may be formed by ananisotropic etching process so as to have a pyramid structure positionedover the semiconductor substrate 100. Also, the variable resistancemember 184 may be separated from the third plug 166 by a given interval.

A third conductive layer 186 is formed on the second insulatinginterlayer 160 to enclose the third plug 166 therein and to cover thevariable resistance member 184. The third conductive layer 186 may beformed with exemplary conductive materials containing nitrogen, a metalor a metal silicide such as was described previously with respect toFIG. 7G, and which are not repeated here for reasons of brevity.

Referring to FIG. 9C, the third conductive layer 186 may be partiallyetched by a photolithographic process to form a first electrode 187 anda second electrode 190 on the second insulating interlayer 160 andlateral portions of the variable resistance member 184. The firstelectrode 187 extends from the third plug 166 to a first lateral portionof the sloped variable resistance member 184, and the second electrode190 extends from a second portion of the sloped variable resistancemember 184 to a corresponding second portion of an adjacent slopedvariable resistance member 184. Thus, two adjacent sloped variableresistance members 184 includes together one second electrode 190 as acommon electrode. The first and second electrodes 187 and 190 enclosethe first and second lateral portions of the sloped variable resistancemember 184, respectively. Here, an upper face of the sloped variableresistance member 184 may be partially exposed between the first andsecond electrodes 187 and 190.

After a third insulating interlayer 196 is formed on the secondinsulating interlayer 160 to cover the first electrode 187, the secondelectrode 190 and the variable resistance member 184, the thirdinsulating interlayer 196 may be partially etched to form a fourthcontact hole 199 that partially exposes the second electrode 190. Thethird insulating interlayer 196 may be formed using TEOS, USG, SOG,HDP-CVD oxide, etc., alone or in a mixture thereof.

Referring to FIG. 9D, a fourth conductive layer may be formed on thethird insulating interlayer 196 to fill the fourth contact hole 196, soas to form a fourth plug 202 and an upper wiring 205 and to complete theexemplary phase-change memory device with sloped variable resistancemember 184. The fourth plug 202 contacting the second electrode 190 maybe formed in the fourth contact hole 199, with the upper wiring 205formed on the third insulating interlayer 196. The fourth plug 202electrically connects the upper wiring 205 to the second electrode 190.The fourth plug 202 and the upper wiring 205 may be formed of apolysilicon doped with impurities, tungsten, copper, aluminum, tantalum,etc.

According to the exemplary embodiments of the present invention, thephase-change memory device may operate using a relatively low currentwithout deterioration of a phase-change layer thereof and dissipation ofa heat generated in the phase-change layer, since the phase-changememory device includes a variable resistance member that has a self-heatconfined structure. Additionally, because a phase-change region of thephase-change pattern layer is separated from the electrodes, thephase-change pattern layer may not be detached from the electrodes.

Thus, the exemplary phase-change memory device described in thespecification may have cost advantages over conventional DRAM, flashmemory, etc., and even the conventional phase-change memory device, dueto its substantially small active storage media and simpler devicestructure. The exemplary manufacturing method for the phase-changememory device requires fewer steps, resulting in reduced cycle times,fewer defects and potentially greater manufacturing flexibility. As anexample, since two adjacent phase-change memory devices share a commonelectrode, cycle time and manufacturing cost may be reduced Smallerstorage area and cell volume may result in smaller die sizes without theincreasingly exaggerated topologies of conventional memory devices,thereby producing more memory circuits or devices per wafer.

The exemplary embodiments of the present invention being thus described,it will be obvious that the same may be varied in many ways. Suchvariations are not to be regarded as departure from the spirit and scopeof the exemplary embodiments of the present invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1.-12. (canceled)
 13. A method of manufacturing a phase-change memorydevice, comprising: forming a variable resistance member on asemiconductor substrate having a contact region; forming a firstelectrode to contact a first portion of the variable resistance memberand to be electrically connected to the contact region; and forming asecond electrode to contact a second portion of the variable resistancemember.
 14. The method of claim 13, wherein forming the variableresistance member includes: forming a first insulation layer pattern onthe semiconductor substrate; forming a phase-change layer pattern on thefirst insulation layer pattern; and forming a second insulation layerpattern on the phase-change layer pattern.
 15. The method of claim 14,wherein forming the variable resistance member further includes: forminga first insulation layer on the semiconductor substrate; partiallyetching the first insulation layer to form the first insulation layerpattern; forming a phase-change layer on the semiconductor substrate tocover the first insulation layer pattern; partially etching thephase-change layer to form the phase-change layer pattern; forming asecond insulation layer on the semiconductor substrate to cover thephase-change layer pattern; and partially etching the second insulationlayer to form the second insulation layer pattern.
 16. The method ofclaim 14, wherein forming the variable resistance member furtherincludes: forming a first insulation layer on the semiconductorsubstrate; forming a phase-change layer on the first insulation layer;forming a second insulation layer on the phase-change layer; andsequentially etching the second insulation layer, phase-change layer andfirst insulation layer to form the second insulation layer pattern,phase-change layer pattern and first insulation layer pattern.
 17. Themethod of claim 16, wherein the second insulation layer, phase-changelayer and first insulation layer are anisotropically etched.
 18. Themethod of claim 13, wherein forming of the first electrode and secondelectrode is performed simultaneously.
 19. The method of claim 18,wherein forming the first and the second electrodes includes: forming aconductive layer on the variable resistance member; and partiallyetching the conductive layer to simultaneously form the first and secondelectrodes. 20.-26. (canceled)
 27. A method of manufacturing aphase-change memory device, comprising: forming a contact region on asemiconductor substrate; forming a lower wiring on the semiconductorsubstrate to electrically contact the contact region; forming a variableresistance member on the semiconductor substrate so as to be separatedfrom the lower wiring; forming a first electrode electrically connectedto the lower wiring and contacting a first portion of the variableresistance member; forming a second electrode that contacts a secondportion of the variable resistance member and a portion of an adjacentvariable resistance member; and forming an upper wiring electricallyconnected to the second electrode. 28.-29. (canceled)
 30. A method ofmanufacturing a phase-change memory device, comprising: forming avariable resistance member on a semiconductor substrate having a contactregion; forming a first electrode so as to enclose a first lateralportion of the variable resistance member, the first electrodeelectrically connected to the contact region; and forming a secondelectrode so as to enclose a second lateral portion of the variableresistance member.